As heretofore, a need exists for fiber goods with improved absorbency in the field of sanitary products, medicine, household articles, clothing and technical applications. Thereby, the more and more stringent physiological requirements, in particular in the areas of sanitary products and medicine, limit the possibilities of a selection among hydrophilic fiber modifications to a considerable extent. Viscose fibers modified to be hydrophilic are known under the tradename Viscosorb (cf. Lenzinger Berichte, Issue 51, 1981, page 34ff). Even though they meet the requirements of Deutsches Arzneibuch (German Pharmacopoeia, hereinafter "DAB") and Europaesches Arzneibuch (European Pharmocapoeia, hereafter "EAB") to some extent, their water retentivity still is in need of improvement.
Cellulose acetates, in the form of amorphous products and fibers, have been known for a long time. Acetate fibers are prepared with an acetic acid content of about 53 to 55%, which corresponds to a degree of esterification of 2.3. At a degree of esterification of 1.2 to 3, the known cellulose acetates are water-insoluble, but at the lower degrees of esterification of 0.6 to 0.9 they are soluble in water (cf. Ullmann, Vol. 9, 4th Edition, 1975, table 4, page 233 and page 238) and Ott et al Cellulose and Cellulose Derivatives, 2nd Ed., Part III, Interscience Publishers, Inc., 1955, pages 1076-7 and 1460. The known cellulose acetates with degrees of esterification in the range of 1.2 to 1.8 are also soluble in 2 methoxyethanol (Ullman, ibid.).
Previously, cellulose esters with low acetic acid content, such as involved here, were obtained through hydrolysis via the triester stage. The excess of anhydride was destroyed by the addition of water and a certain number of acetyl groups was split off again by the addition of more sulfuric acid. The consumption of acetic anhydride and sulfuric acid was correspondingly high (Ullmann, Vol. 9, 1975, pages 228 and 230).
It is the goal of the present invention to make available new water-insoluble fibers with an improved absorbency for water and physiological liquids, which, in addition, also meet the increased physiological demands in the areas of sanitary products and medicine.
The objects of the invention are water-insoluble fibers of cellulose acetate, cellulose propionate and cellulose butyrate, with an extremely high absorptive capacity for water and physiological liquids, which are characterized by the fact that they exhibit
(a) in the sequence as mentioned, a degree of esterification of 0.1 to 1.5, 0.1 to 0.95 and 0.15 to 0.8. PA1 (b) an average degree of polymerization from 300 to 700; PA1 (c) a fiber strength in the conditioned state of 6 to 20 cN/tex; PA1 (d) an elongation in the conditioned state of 6 to 20%; PA1 (e) a water retentivity of 200 to 750%; and PA1 (f) a wicking capacity for water of 8 to 18 cm/g of fiber.